IRP-10
Proceedings of 12th ISMAS Symposium cum
Workshop on Mass Spectrometry
On Line Determination of Deuterium in Hydrogen Water
Exchange Reaction by Mass Spectrometry
J. D. Sharma, K. P. Alphonse, Sushama Mishra, S. A. Prabhu,
Sadhana Mohan and V. K. Tangri
Heavy Water Division, Bhabha Atomic Research Centre,
Trombay, Mumbai-400 085, INDIA
Email : [email protected]
Introduction
The Deuterium (D)/ Hydrogen (H) analysis at low Concentration is generally carried
out by Mass Spectrometry. Mass Spectrometer is specially designed for the measurement of
Mass 2 and 3 ratio. The Deuterium analysis of water and hydrogen in concentration range of
a few ppm to about 1% plays an important role in the Heavy Water Production Plants [1]. For
the enrichment of the Deuterium concentration in H2O (l) by H2 – H2O exchange a catalyst is
essential as reaction is relatively slow. Heavy Water Division has developed in house
Platinum based catalyst for the isotopic exchange of Hydrogen and Water [2].
An on line Deuterium gas sampling system, which can directly be attached to Mass
Spectrometer, was developed for carrying out the catalyst performance. Performance of the
catalyst was studied in Static as well as in the Dynamic mode. Over all isotopic exchange
reaction between Deuterated water and Ultra pure Hydrogen gas is taking place in the
presence of the catalyst and ceramic raschig ring. Ceramic raschig rings act as hydrophilic
agent where as, Platinum loaded on activated charcoal mixed with Teflon in raschig rings
form behaves as hydrophobic catalyst [3,4]. Liquid water is converted to water vapour over
hydrophilic packing and deuterium exchange between H2O (v) and hydrogen gas is taking
place over the catalyst surface.
HDO + H2
HD + H2O
Specific activity [5,6] of the catalyst kv* was calculated by knowing Deuterium
concentration of H2 gas and liquid water, weight of the catalyst, superficial gas velocity &
liquid flow.
The upper limit of analysis is restricted to 1 % Deuterium concentration due to mass 4
interference and memory problem associated with higher deuterium concentration.
Experimental
[A] A double collector Mass Spectrometer indigenously manufactured by Technical
Physics & Prototype Engineering Division of B.A.R.C, Mumbai was used for this work.
[B] Catalyst Preparation
Platinum loading on activated carbon was done by impregnation of carbon with
chloroplatinic acid. After impregnation this was reduced with high purity Hydrogen gas at
3500 C. This platinum loaded carbon was homogeneously mixed with Teflon and compacted
to raschig ring form of size 6mmX6mmX3mm. The final composition of the catalyst is 0.1%
Pt, 0.9% C, 99% Teflon.
12th ISMAS-WS-2007, March 25-30, 2007, Cidade de Goa, Dona Paula, Goa
Proceedings of 12th ISMAS Symposium cum
Workshop on Mass Spectrometry
IRP-10
[C] Static System
A static system made up of stainless steel was designed and fabricated in Heavy Water
Division workshop for carrying out the isotopic exchange, to eliminate the problem of
handling glass system as shown in figure-1.
Fig-1. Stainless Steel Static Sample Bottle
The sample bottle shown in figure-1 was dried in an oven for 2 Hrs. at 1100 C and
cooled down to room temperature. A known quantity of ceramic raschig ring and platinum
loaded catalyst was taken inside the sample bottle. Ultra pure Hydrogen gas was taken at a
pressure of 1.2 Kg/cm2 in the sample bottle after repeated flushing and evacuating the system.
Isotopic purity of hydrogen gas was analyzed by Mass Spectrometer. 1.2 ml of Heavy Water
(500 ppm) was injected into system and Deuterium concentration was analyzed on Mass
Spectrometer at regular intervals. The time taken for half of the equilibrium concentration
was measured from the plot of Time vs Deuterium concentration measured (Figure - 3) on
Mass Spectrometer.
[D] Dynamic System
Catalyst column containing 50% each hydrophobic catalyst and ceramic raschig ring
was (Figure-2) packed in the glass column. Heavy water (1000ppm) was passed downwards
through the mixed bed and hydrogen gas saturated with water vapour was allowed to flow
counter currently up wards. From the known deuterium (D) concentration of water entering
the column at the top, D concentration of Hydrogen at top and bottom was analyzed on line
with the help of mass spectrometer. Water enriched in deuterium concentration entering and
leaving the column was separately analysed for their D/H ratios after converting into H2 over
a furnace attached to the mass spectrometer.
12th ISMAS-WS-2007, March 25-30, 2007, Cidade de Goa, Dona Paula, Goa
IRP-10
Sr.
No
1
2
3
4
5
6
7
8
9
Time
in Min
0
5
10
15
20
30
60
90
180
D Conc.
in PPM
28.7
41.3
52.7
60.9
67.9
80.4
90.7
100.1
112.6
Table – I Change in D conc. With time
Deuterium conc. in ppm
Proceedings of 12th ISMAS Symposium cum
Workshop on Mass Spectrometry
120
100
80
60
T1/2
40
20
0
0
50
100
150
200
Time in minutes
Fig. 3 T1/2 Measurements for static set up
Results & Discussion
From the static experiments it was found that T1/2, the time taken to reach half the
equilibrium concentration is 22 minutes (Figure-3) for 10 gms of catalyst.
The online static system developed for deuterium analysis in H2 gas by Mass
Spectrometry is easy to operate and no glass handling is involved. The quantity of gas
required for mass spectrometeric analysis is also reduced as the system was directly
connected to mass spectrometer for analysis through narrow tubing. As sample volume drawn
from the system for analysis is considerably reduced pressure drop in the reactor vessel is
also reduced.
The catalyst activity was measured in dynamic system as follows:
12th ISMAS-WS-2007, March 25-30, 2007, Cidade de Goa, Dona Paula, Goa
Proceedings of 12th ISMAS Symposium cum
Workshop on Mass Spectrometry
IRP-10
The specific activity of the catalyst was measured as the overall gas-phase volume transfer
rate kv* given in the s-1.
F
kv* = --- x NTU
H
Where F= superficial hydrogen flow rate in m/s.
H= height of catalyst bed in m
NTU= No. of transfer units in the bed,
( yb- yt )
(yb-yb*)
NTU = -------------------- ln --------(yt-yt* )
( yb-yb*)- (yt-yt*)
y = the atom fraction of D in the Hydrogen gas,
The subscript t and b refers to the top and bottom of exchange column and the superscript (*)
denotes the D conc. in the hydrogen in equilibrium with the water. The value of y* is
calculated from the exact relation
x
y*= ------------α -x (α -1)
Where x = the atom fraction of D in the water
α = seperation factor
The specific activity of the catalyst (kv* = 0.02s-1 ) prepared in our Division is found to be in
comparable with similar catalysts.
Acknowledgement
Authors are grateful to Mr. M. S. Dalvi, Mr. T. M. Gaikwad (for fabrication of static
set up), Mr. A. K. Chatterji, Mr. P. R. Golatkar, Mr. R. N. Patra (for catalyst preparation),
Mr. Deodatta Gaikwad, Mr. R.M.Ghadi (for mass spectrometric analysis), Mr. Sameer
Shinde (for Photography), Mr. S.K.Das, Mr. G.K.Nath, Mr. Rajesh Kumar and Mr. Kalyan
Bhanja (for analytical and technical support).
References
1.S.K. Malhotra, T.Jayaprakash, M.S.Krishanan & H.K.Sadhukhan, 2nd National symposium
on Mass Spectrometry, Dec 21-23, 1981, BARC, Mumbai.
2.S.K.Malhotra, M.S.Krishanan & H.K.Sadhukhan; preprint volume; National symposium
Heavy Water Technology, April 3-5, 1989, CI-2, BARC, Mumbai.
3.W.H.Stevens; Canadian patent 907, 292 (1972).
12th ISMAS-WS-2007, March 25-30, 2007, Cidade de Goa, Dona Paula, Goa
Proceedings of 12th ISMAS Symposium cum
Workshop on Mass Spectrometry
IRP-10
4.W.H.Stevens; et.al; conference Chemical process, volume 56, 22(1972).
5.M.Hammerli; et. al; International journal of Hydrogen Energy Volume 4, 89(1979),
6.R.E.Treybal, Mass transfer operations (sec. ed.), McGraw Hill, N.Y(1968).
12th ISMAS-WS-2007, March 25-30, 2007, Cidade de Goa, Dona Paula, Goa